RRD Graphs - Fix sample lenght

I've been using pfSense for some good 6 months now and something that's bothering me is that some of the graphs are not as nice as the 8 hour graph, as in the width of each column is not equal to one pixel.
Is this something that can be fixed or changed somewhere?

Better examples:

8 Hour graph uses 1 minute samples, equals to 480 samples and as the graph is 480 pixels wide it fits very nicely. This one is perfect.
1 day graph uses 5 minutes samples, equals to 288 samples, it stretches the samples to fill the 480 pixels. This could be changed to 3 minutes samples to be a perfect 1 pixel 1 sample ratio.
Weekly graph uses 1 hour samples, equals to 168 samples, again filling the space with larger columns. This could be 21 minutes samples to fit nicely.
and so on…